The invention relates generally to pressure dissipating systems for high-pressure polyphase fluids, and more particularly to a letdown device adapted to be coupled with a discharge orifice for a coal conversion system and employed in reducing output pressure, without experiencing a temperature drop, flashing or encountering serious erosion resulting from particulates entrained in the fluid.
The term "flashing", as herein employed refers to a phenomenon which may occur during pressure letdown when a liquid evolves into the gas phase. If uncontrolled or not limited, the rapid change in pressure may result in an implosion which can damage a surface such as the interior of a valve, ect.
Further, the term "entrainment", as herein employed, refers to a condition of flow of a fluid in which all components (solid, liquid, and/or gas) are maintained at the same velocity.
As is well known, polyphase fluids emerging from coal conversion systems usually consist of a flashable lliquid, which tends to evolve into a gas, transporting extremely hard and erosive particulate solids. Such fluids, when emerging from coal conversion systems are characterized by not only high temperatures but also high pressures. As a consequence of the damage resulting from the effects of the erosive solids and liquid flashing, the longevity of the plumbing utilized in handling such polyphase fluids is brief. Even so, in processes such as coal liquefaction, it is imperative that pressures be letdown or dropped while, preferably, maintaining constant enthalpy.
Since separation of the phases of the polyphase fluids results in detrimental differences in the flow velocities for the different phases, as well as an excessive distribution of velocities in the bulk flow, it is necessary in order to minimize damage that entrainment of the phases be maintained, whereby a common velocity may be imposed on all phases of the fluid.
As also is well known, in one form of coal conversion, gasification, the process tends to produce large quantities of high-pressure polyphase fluids including solids, liquids, and gasses, at temperatures approximating one thousand (1,000) degrees F. at pressures of approximately 3000 PSI.